Abstract
We have used the focused, polychromatic beam available at sector 34 of the APS to characterize the local lattice structure and perfection of several different forms of ZnO meso- and nano-structures. Using Kirkpatrick-Baez mirrors for white-beam focusing, we have developed scanning x-ray techniques capable of mapping the spatially-resolved lattice structure, strain and composition. Off-axis undulator radiation is routinely focused to ~0.5 mm and beams as small as 90 nm have been demonstrated. Laue diffraction patterns are collected using a CCD area detector, and computer analysis provides spatial maps of the crystal phase, grain orientations (texture), and the local strain tensor. We have demonstrated the ability to map the structure of individual meso- and nano-structures using ZnO fabricated in several different shapes: rods, belts and tapered styluses. TEM samples serve as ideal x-ray microdiffraction samples due to the low background signal. Even when mounted on a relatively-thick crystal substrate, full diffraction patterns can be measured from ZnO rods as narrow as 200 nm diameter. We find that all of the ZnO structures have a facetted, hexagonal crystal structure, with the c-axis often along the rod axis. Larger diameter rods are essentially perfect single crystals, wheras thinner rods show a high degree of flexibility and hence large local mosaic spread along the rod axis. For stylus samples, the tapered region where the diameter decreases remains a single crystal.
